As a consequence of many factors, including demand for increased portability, computing power and energy efficiency in modern electronics, integrated circuits are continuously being reduced in size and the density of electrical devices, e.g., capacitors and transistors, in these integrated circuits are constantly increasing as a result of this size reduction.
The trend of increasing electrical device densities is evident, for example, in memory circuits such as dynamic random access memories (DRAMs), static random access memories (SRAMs), ferroelectric (FE) memories, etc. To take one example, DRAM is typically fabricated by forming millions of identical circuit elements, known as storage or memory cells, on a single semiconductor wafer. Each of these cells is an addressable location that can store one bit (binary digit) of data. In its most general form, a memory cell typically consists of two electrical devices: a storage capacitor and an access field effect transistor. By increasing the density of these electrical devices, the memory cell density of these memory circuits can be increased, thereby increasing the storage capacity of a single memory chip.
As part of this trend of increasing electrical device density, there is constant pressure to decrease the feature size or area occupied by these devices, such as capacitors, to allow for further increases in device density. Nevertheless, capacitors must have a capacitance large enough to retain a certain minimum charge, as determined by design and operational parameters, to ensure reliable operation of the memory cell. Because capacitors are, most generally, two electrodes on either side of a dielectric and because capacitance is proportional to the surface areas of opposing electrodes, one way to increase the capacitance of a memory cell capacitor, while minimizing the area occupied by the capacitor, is to increase the surface area of the lower electrode of the capacitor. For this purpose, hemispherical grain (HSG) silicon, which forms a convoluted surface with numerous protrusions, has been used to increase the surface area of the lower electrode of capacitors.
While capacitors using HSG silicon for electrodes have allowed further increases in device densities, increasing device densities have also made integrated circuits more susceptible to shorts between devices. In particular, it has been found that neighboring capacitors in memory circuits are particularly prone to electrical shorts between their bottom electrodes.
Accordingly, there is a need for methods of preventing electrical shorts between electrical devices such as capacitors.